(MCT) — CHICAGO — More than two years after reopening the John Wayne Gacy case, Cook County, Ill., sheriff’s investigators continue to probe cold case files from across the country and leads closer to the home in search of additional victims of the notorious serial killer who was executed nearly two decades ago.

Among the investigative avenues investigators are now pursuing is the case of two teenage boys who were raped and slain in Michigan in the 1970s when Gacy’s killing was at its height and he was believed to have traveled to Michigan. Sheriff Tom Dart said in a speech Tuesday that investigators are trying to determine if a DNA match can be made while also studying Gacy’s travel records.

Dart would not reveal details of the Michigan case but said it was high-profile. Authorities in Michigan had contacted Dart’s office.

“We’re working on that case as we speak to see if we can match his blood to some of the evidence that was taken at the crime scene,” Dart said in his remarks at the City Club of Chicago. “I always found it beyond credibility to think he didn’t murder elsewhere based on the fact he was such a monster.”

At the same time, the investigators are examining a case from the East Coast, while also planning to do work in the backyard of a building in Chicago’s Northwest Side, where Gacy’s mother lived at one time and where witnesses have said they noticed unusual activity. Workers will scan the ground for anomalies and, if they are found, will drill small holes so cadaver dogs can sniff the area.

Workers scanned the yard and excavated spots in 1998, but an extensive dig was not conducted in spite of finding numerous anomalies. The new work probably will not take place until early in the spring, according to Frank Bilecki, a spokesman for the sheriff’s department.

Since the sheriff’s reopening of the Gacy case was made public, the office has received about 150 leads. About half of them have been closed. Seven people who were missing have been identified — five of them alive, two dead, though neither had a connection to Gacy. Twenty-seven cases are being worked on, while another 28 cases are in earlier stages of evaluation. Twenty have been determined to have no relation to Gacy, said Bilecki.

Gacy was linked to the murders of 33 boys and young men in the mid-1970s, most of them discovered in the crawlspace of his home in Norwood Park Township. Convicted and sentenced to death, he was executed by lethal injection in 1994 and was never linked to additional victims.

The sheriff’s office submitted Gacy’s DNA profile to a national database late last year.

According to Dart, Gacy’s travel records were “never really thoroughly examined,” and his office is working with the FBI to determine if Gacy’s “extensive travel history” matches open cases across the country. If it does, sheriff’s investigators plan to review those cold case files. Dart pointed to a Florida man who said Gacy, posing as a police officer, tried to attack him. The man told investigators that he escaped, but not before throwing his wallet at Gacy.

The man’s name was found on a driver’s license inside Gacy’s home, Dart said.

““How is it that you can imagine that someone who killed at the level this person did was not killing elsewhere?” Dart said at the City Club. “And why would we not be reaching out and making sure we’ve exhausted ... basic stuff?”